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Biological control offorest insect pests 219
of pest outbreaks (examples are treatments to control M. disstria and L. dispar) ,
whereas in most other cases the bacterium was applied with aerial sprays (examples
here include attempted control of C. fumiferana, C. occidentalis, and O.
pseudotsugata). Most development of aerial spraying of B.t. was conducted with C.
fumiferana. Both water-based and oil-based formulations were used and the spray
aircraft included fixed-wing aircraft equipped with from one to four engines, and
various sizes of helicopters. Areas treated ranged as high as 90 000 ha, and in all cases
results to a large extent depended on the application techniques that were employed.
The time period during which B.t. can be applied during the insects' development is
shorter than that permissible with chemical insecticides because the bacterium must be
ingested to be effective whereas the standard chemical insecticides are neurotoxins and
exhibit contact toxicity. An interesting international aspect of this work involved cooperative
trials between Canada and the United States under the 6-year CAN USA
Spruce Budworms Research Programme that started in 1977. The two countries also cooperated
in one trial using B.t. against O. pseudotsugala in British Columbia.
The use of viruses, particularly baculoviruses, for control of forest insect pests has
progressed rapidly since the last review, and Morris (1980) provides a convenient
tabulaton of all field tests where either ground or aerial applications of virus were used.
Most attention has been focused on the neodiprionid sawflies because NPVs that attack
these sawflies were found to be particularly virulent. Many sawflies also feed colonially,
which facilitates cross infection, and some of the viruses spread from the point of
infection, thus allowing spot introductions of virus to be used rather than complete
coverage of the infected areas. Predacious and scavenging insects are thought to be the
main disseminators of the viruses. In some cases strips of the infected area were
sprayed, and in the case of N. swainei spot introductions of laboratory-infected pupae
were used. Other viruses, again mainly NPVs, with good virulence against a number of
Lepidoptera, have also been evaluated. Examples are tests against the tussock moths,
O. leucostigma, and O. pseudotsugata. Some less virulent viruses were also applied
aerially against, for example, C. fumiferana and C. occidenlalis; others were applied by
ground sprays. for example. those against M. disstria and L. dispar.
The remaining entomopathogens covered in this review are essentially at the laboratory
stage of development. Fungi are well known to cause epizootics, such as the one
believed to have helped collapse a recent outbreak of hemlock looper, Lambdina
fiscellaria fiscellaria (Guenee), in Newfoundland (Otvos 1973). Other North American
forest pests in which fungal epizootics have been recorded include spruce budworm C.
fumiferana, black headed budworm, Acleris variana (Fern), and forest tent caterpillar,
M. disslria. Entomophthora spp. of fungi are generally responsible and these are the
fungi on which the Canadian Forestry Service concentrates its effort. Much of the
biology of these fungi is now elucidated; before direct applications are attempted, efforts
continue to devise techniques for mass production of resting spores, to devise practical
application systems, and to induce spore germination, particularly under field conditions.
One study, not reported elsewhere in this review, is an examination of control possibilities
of mountain pine beetle, Dendroctonus ponderosae Hopkins, with Beauveria bassiana
Vuillemin. This work can be summarized by stating that although the fungus is lethal to
the insect in laboratory trials, no satisfactory way has yet been found to infect insects in
the field (S. Whitney2 1981, personal communication).
Work with protozoa roughly parallels that with fungi and emphasis is now on epizooticlogical
studies. Protozoa are dominant entomopathogens of insects such as spruce
budworm, C. fumiferana, but their effects are to debilitate rather than to kill the insects,
by affecting larval and pupal vigour and by reducing adult longevity and fecundity.
Because these entomopathogens are ubiquitous. work continues to elucidate their
interaction with other control agents.
2 Pacific Forest Research Centre, Victoria. British Columbia.